linux-kernel - Re: [RFC] treewide: cleanup unreachable breaks

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Date:   Sat, 17 Oct 2020 14:01:22 -0700
From:   Dan Williams <dan.j.williams@...el.com>
To:     trix@...hat.com
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
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Subject: Re: [RFC] treewide: cleanup unreachable breaks

On Sat, Oct 17, 2020 at 9:10 AM <trix@...hat.com> wrote:
>
> From: Tom Rix <trix@...hat.com>
>
> This is a upcoming change to clean up a new warning treewide.
> I am wondering if the change could be one mega patch (see below) or
> normal patch per file about 100 patches or somewhere half way by collecting
> early acks.
>
> clang has a number of useful, new warnings see
> https://clang.llvm.org/docs/DiagnosticsReference.html
>
> This change cleans up -Wunreachable-code-break
> https://clang.llvm.org/docs/DiagnosticsReference.html#wunreachable-code-break
> for 266 of 485 warnings in this week's linux-next, allyesconfig on x86_64.
>
> The method of fixing was to look for warnings where the preceding statement
> was a simple statement and by inspection made the subsequent break unneeded.
> In order of frequency these look like
>
> return and break
>
>         switch (c->x86_vendor) {
>         case X86_VENDOR_INTEL:
>                 intel_p5_mcheck_init(c);
>                 return 1;
> -               break;
>
> goto and break
>
>         default:
>                 operation = 0; /* make gcc happy */
>                 goto fail_response;
> -               break;
>
> break and break
>                 case COLOR_SPACE_SRGB:
>                         /* by pass */
>                         REG_SET(OUTPUT_CSC_CONTROL, 0,
>                                 OUTPUT_CSC_GRPH_MODE, 0);
>                         break;
> -                       break;
>
> The exception to the simple statement, is a switch case with a block
> and the end of block is a return
>
>                         struct obj_buffer *buff = r->ptr;
>                         return scnprintf(str, PRIV_STR_SIZE,
>                                         "size=%u\naddr=0x%X\n", buff->size,
>                                         buff->addr);
>                 }
> -               break;
>
> Not considered obvious and excluded, breaks after
> multi level switches
> complicated if-else if-else blocks
> panic() or similar calls
>
> And there is an odd addition of a 'fallthrough' in drivers/tty/nozomi.c
[..]
> diff --git a/drivers/nvdimm/claim.c b/drivers/nvdimm/claim.c
> index 5a7c80053c62..2f250874b1a4 100644
> --- a/drivers/nvdimm/claim.c
> +++ b/drivers/nvdimm/claim.c
> @@ -200,11 +200,10 @@ ssize_t nd_namespace_store(struct device *dev,
>                 }
>                 break;
>         default:
>                 len = -EBUSY;
>                 goto out_attach;
> -               break;
>         }

Acked-by: Dan Williams <dan.j.williams@...el.com>